Process for making expandable vinyl aromatic resin compositions



March 20, 1962 E. F. ENGLES 3,025,273

PROCESS FOR MAKING EXPANDABLE VINYL AROMATIC RESIN COMPOSITIONS OriginalFiled Nov. 29, 1957 v D INVENTOR. Ear/K 6/79/66 ATTORME rs United StatesPatent ()fitice 3,025,233 Patented Mar. 2%, 1952 3,026,273 PROCESS FORMAKING EXPANDABLE VlNYL ARGMATIC RESIN COMPOSITIGNS Earl F. Engles,Midland, Mich assignor to The Dow Chemical Company, Midland, Mich., acorporation of Delaware Continuation of application Ser. No. 699,666,Nov. 29, 1957. This application May 8, 1961, Ser. No. 110,608 11 Claims.(Cl. 260-25) This invention concerns a process for making expandablethermoplastic resin compositions. It relates more particularly to aprocess for making polymeric compositions comprising essentially anormally solid thermoplastic vinyl aromatic resin having a volatileorganic compound uniformly dispersed throughout which compositions arecapable of expanding upon heating to form cellular masses.

It is known to make cellular or foamed plastic masses by incorporating avolatile organic liquid or a solid substance which decomposes under theaction of heat to form a gas, with a thermoplastic material andthereafter to heat the material at elevated temperatures whereby the gasor vapors of the volatile liquid expand the thermoplastic material toform a cellular or porous mass.

US. Patent No. 2,681,321 makes porous plastic masses by incorporatingwith a thermoplastic polymer a volatile organic liquid in which thepolymer is insoluble such as petroleum ether, pentane, hexane, heptane,methyl alcohol, acetone, dipropyl ether and the like, either by soakingor swelling the solid polymer, e.g. polystyrene, in the volatile organicliquid, or by dissolving the volatile organic liquid in the monomer or amixture of the monomer and polymer and heating the mixture at atemperature below the boiling point of the volatile organic liquid underthe conditions employed, to obtain a solid polymeric body containing thevolatile liquid dispersed throughout, then heating the solid material toa temperature above its softening point and above the boiling point ofthe volatile liquid whereby a porous polymer mass is obtained.

The method heretofore proposed for making polymeric compositionssuitable for use in the manufacture of porous or cellular plastic masseshave not been entirely satisfactory because soaking of the solid polymerin the volatile organic liquid frequently requires maintaining thepolymer in contact with the organic liquid for prolonged periods of timein order to obtain a product having the volatile liquid uniformlydispersed throughout. The polymerizing of monomers in admixture withmany volatile organic liquids in which the polymer is insoluble or onlyswellable, increases the problems of manufacture, requires the use ofpressure resistant polymerization vessels and in many instances thevolatile organic liquid tends to inhibit the polymerization reaction.

It has now been found that expandable thermoplastic 'resin compositionscomprising essentially a thermoplastic vinyl aromatic resin having avolatile organic compound uniformly dispersed throughout can readily beprepared by supplying a mixture of a heat-plastified thermoplasticpolymer and a volatile organic compound under superatmospheric pressureat temperatures between 160 and 280 C. to a mixing and cooling zone,advancing the mixture toward an extrusion orifice or die, cooling andblending the mixture during said advancing to a homogeneouslyheat-plastified mass at temperatures between 90 and 130 C., extrudingthe heat plastified mass into a zone of substantially atmosphericpressure and almost immediately contacting the extruded material with aninert liquid cooling medium at a temperature below 50 C. and withdrawingthe extruded material from the orifice face.

The invention is described more particularly with reference to theaccompanying drawing wherein is shown partly in section one of thevarious forms of arrangements of apparatus which can be used in practiceof the invention. The drawing shows a longitudinal section through thebarrel of a plastics extruder having a first heating and pressingsection, a second mixing and cooling section, a sealing plate betweensaid first and second sections for preventing counter-current leakage ofgas or vapors through the plastics extruder and an extrusion die ororifice for discharging material from the mixing and cooling zone into azone of substantially atmospheric pressure wherein the extruded materialis drawn away from the die face and almost immediately cooled. Thecooled material is usually cut or broken to a granular form.

In the drawing, the numeral 1 designates a feed screw of the compressiontype rotatably mounted in the cylindrical barrel 2 of a horizontalplastics extruder. The screw 1 has a sealing plate 3 Which can be aperforated plate or an annular ring, suitably attached to the midsection and preferably an integral part of the screw. The barrel 2 ofthe plastics extruder is provided with an inlet 4 positioned beyond thesealing plate 3 for feed of a volatile organic compound into the mixingand cooling section. The barrel 2 is surrounded by chambers 5 and 5a forheating or cooling as required, such heating or cooling being carriedout by passage of a heat transfer medium such as steam, air, oil, Wateror brine through the chambers 5 and 5a via suitable inlets and outlets.The screw 1 is provided with a terminal mixing torpedo 6 suitably of atype similar to that described in US. Patent No. 2,45 3,088. Beyondmixing torpedo 6 in the eX trusion path is a screen or strainer 7 heldin place across the discharge end of the barrel 2 by head 8 which issecured to the body of the plastics extruder by any suitable means, e.g.bolts. Head 8 can be of any desired form and may be straight or curvedas shown. The head 8 provides a continuation of the extrusion path andterminates with an extrusion die 9 containing one or a plurality ofconstricted passageways for discharging the extruded material. Theextruded material is drawn away from the die 9 in the form of one or aplurality of strands or as a ribbon or sheet and is almost immediatelycontacted with an inert liquid cooling medium 10 in vessel 11 whereinthe extruded material is cooled, then is Withdrawn and passed to cuttingdevice 12 and cut to a granular form. The material need not be cut to agranular form as cooled, but can be drawn away as a sheet or strands.

In producing a latent-foaming polystyrene composition by the method ofthe invention, granular polystyrene, suitably having a molecular weightcorresponding to a viscosity characteristic of from 15 to 30 centipoisesor higher as determined for a 10 weight percent solution of thepolystyrene in toluene at 25 C., is fed into the first heating andpressing section of the plastics extruder wherein the polystyrene isheat-plastified or melted, e.g. is pressed and heated to temperaturesbetween and 280 C., and is brought to a plastic flowable condition. Theheat-plastified polystyrene is pressed by the flights of screw 1 in thebarrel 2 of the extruder and forced through, if perforated, or aroundsealing plate 3 into the second or mixing and cooling section of theextruder. A volatile organic compound, e.g. petroleum ether, isopentane,dichlorodifluoromethane or the like, in which the polystyrene issubstantially insoluble or only swellable is fed to the mixing andcooling section of the extruder via inlet 4 under pressure and in thedesired amount into admixture with the heat-plastified polystyrene. Theresulting mixture is forwarded and blended by flights of the screw andthe terminal mixing torpedo 6 and is brought to a desired temperature,suitably between 90 and 130 C, by passage of a heat transfer mediumthrough chamber 5a and is forced through the strainer 7 into head 3 anddischarged through die 9 into a zone of substantially atmosphericpressure. The extruded material is allowed to fall away by gravity orpreferably is drawn away at about the rate of extrusion through die 9 ora somewhat greater rate, and is almost immediately contacted with aninert liquid coolant 10, suitably water or brine and cooled to atemperature below C., after which the material is withdrawn from thecooling liquid and passed to cutting device 12 wherein it is cut to agranular form.

Although the invention is particularly described with reference to themaking of latent-foaming polystyrene compositions, the process can beapplied to any thermoplastic resin and volatile organic compound inwhich the resin is insoluble or substantially insoluble or which onlyswells the resin.

More specifically, the process can be employed to make latent-foamingpolymeric compositions from the normally solid thermoplastic polymers ofone or more monovinyl aromatic compounds of the benzene series, i.e.containing a single vinyl radical directly attached to a carbon atom ofsaid benzene nucleus, such as styrene, vinyltoluene, vinylxylene,ethylvinylbenzene, isopropylstyrene ar-ethylvinyltoluene, di-tert-butylstyrene or nuclear halogenated derivatives of such monovinyl aromatichydrocarbons, e.g. chlorostyrene, dichlorostyrene, bromostyrene, orfluorostyrene. Thermoplastic copolymers of from 99.9 to 99.99 percent byweight of any one or more such monovinyl aromatic compounds and from 0.1to 0.01 percent of a polyvinyl aromatic hydrocarbon such asdivinylbenzene, ethyldivinylbenzene, divinyltoluene or divinylxylene canalso be used. Other thermoplastic copolymers that can be employed in theprocess are copolymers of from to 99 percent by weight of one or moremonovinyl aromatic compounds and from 30 to 1 percent of an alkenylaromatic compound such as alphamethyl styrene, para-methyl-alpha-methylstyrene or alpha-ethyl styrene, or copolymers of from-70 to 99 percentby weight of a monovinyl aromatic compound, e.g. styrene, vinyltoluene,dichlorostyrene and the like, and from 30 to 1 percent of acrylonitrile,methyl methacrylate, acrylic acid or methacrylic acid.

The volatile organic compound to be employed as the foaming agent in theprocess can be a liquid or gas at ordinary temperatures and pressures,i.e. at atmospheric conditions, and to be best suited forthe purpose ofthe invention is a non-solvent or poor solvent for the polymer and has aboiling point not substantially higher than the softening point of thepolymer. Suitable volatile organic compounds are the saturated aliphatichydrocar- 1 bons containing from 4 to 7 carbon atoms in the molecule andperchlorofluorocarbons which compounds have a molecular weight of atleast 58 and a boiling point not higher than C. at 760 millimetersabsolute pressure.

Examples of such volatile organic compounds are butane, n-pentane,isopentane, neopentane, hexanes, heptanes, trichlorofiuoromethane,dichlorodifluoromethane, 'monochlorotrifiuoromethane, symtetrachlorodifluoroethane. 1,2,2-trichloro 1,1,2 trifiuoroethane,sym-dichlorotetra fiuoroethane, 1 chloro 1,l,2,2,2 pentafiuoroethane, 1-chloro 1,2,2,3,3,4,4 heptafiuorocyclobutane and1,2dichloro-1,2,3,3,4,4-hexafiuorocyclobutane. Mixtures of any twoormore of such volatile organic compounds can also be used. 7

The volatile organic compound can be employed in amounts correspondingto from 0.05 to 03, preferably from 0.05 to 0.2, gram molecularproportions of thej volatileorganic compound per grams of the polymericmaterial. The volatile organic compound is preferably calculated on agram molar basis per 100 grams of the polymeric starting material inorder to have present in the final composition an amount of the volatileorganic 4 compound sufiicient to provide an equal or substantially equalvolume of vapors for subsequently expanding the polymer to form acellular mass, regardless of the density of the volatile organiccompound employed.

In practice a normally solid thermoplastic material, e.g. polystyrene, acopolymer of from 99.9 to 99.99 percent by weight of styrene and from0.1 to 0.01 percent of divinylbenzene or a copolymer of from 70 to 99percent by weight of styrene and from 30 to 1 percent of acrylonitrile,alpha-methyl styrene or methyl methacrylate, is fed to a plasticsextruder having a heating and pressing section, a mixing and coolingsection, a sealing plate interposed between said sections and inlets forfeeding materials to said sections and a constricted dischargepassageway or extrusion orifice, similar to the plastics extruder shownin the accompanying drawing. The polymer preferably in granular form ispressed and heated to heat-plastifying temperatures between 160 and 280C. in the first section of the extruder. The heatplastified material isforced by means of the feed screw around or through the sealing plateand into the second or mixing and cooling section of the extruder. Theflow of the heat-plastified polymer around the sealing plate forms aneffective plastic seal against counter-current leakage of gas or vaporsthrough the extruder. A volatile organic liquid, e.g. pentane,dichlorodifiuoromethane, neopentane or the like, is fed under pressureto the mixing and cooling section via a suitable inlet and intoadmixture with the heat-plastified polymer in the desired proportion.The resulting mixture is malaxated under pressure and is cooled to atemperature between 90 and C. to form a homogeneously heat-plastifiedpolymeric composition and is extruded through the die or orifice into azone of substantially atmospheric pressure. The composition isdischarged from the extruder through a die or orifice positionedadjacent to, suitably above, a liquid body of a cooling medium, e.g.brine or water, at temperatures between 0 and 50 C., preferably between10 and 40 C. The extruded material is suitably drawn away from the dieor orifice at about the rate of extrusion through said orifice or at asomewhat faster rate and is almost immediately contacted with thecooling medium, suitably by immersing the extruded material in theliquid coolant or by spraying the cooling liquid on the extrudedmaterial, so as to rapidly cool at least the surface of the extrudedmaterial to a rigid condition. The extruded material is usuallycontacted with the liquid cooling medium for a time sufficient to coolthe composition throughout substantially to the same temperature as thecooling medium after which the-composition is withdrawn and is usuallycut or ground to a granular form. The composition is preferably extrudedto the form of continuous strands, ribbons or thin sheets which canreadily be drawn away from the die and rapidly cooled to a rigidcondition and easily cut or broken to a granular form.

Small amounts of additives such as plasticizers, lubricants, dyes, lightstabilizing agents, antioxidants, or flameproofin-g agents can beincorporated with the polymeric compositions. Such additives are usuallyemployed in amounts of from 0.0-2 to 5 percent by weight or more of thepolymer, but such additives are not required in the to that of thepolymeric composition depending in part upon the kind and proportion ofthe foaming agent and the foaming conditions. By heating granules of thelatentfoaming polymeric compositions in a mold which allows escape ofthe vapors the granules can be foamed and fused together to form aunitary foamed body. By varying the proportion of granules placed in amold of a given size, shaped foamed masses having any desired densitywithin the above stated range can be obtained.

The following examples illustrate ways in which the principle of theinvention has been applied but are not to be construed as limiting itsscope.

EXAMPLE 1 Granular polystyrene containing one percent by weight of whitemineral oil as lubricant which polystyrene had a viscositycharacteristic of 28 centipoises as determined for a weight percentsolution of the polystyrene in toluene at 25 C., was fed to a plasticsextruder at a rate of 30 pounds per hour. The plastics extruder employedin the experiment comprised a four foot long barrel having a 2% inchdiameter screw equipped with a mixing head 4 inches in diameter by 2feet long. The mixing head was similar in design to that described inUS. Patent No. 2,453,088. The screw was fitted with a sealing platepositioned on a mid-section thereof. The extruder had an inlet to thebarrel adjacent to the sealing plate on the screw for feed of a volatileorganic compound into the extruder. The sealing plate formed aconstricted passageway between the melting section and the mixing andcooling section of the extruder so that flow of the molten polystyrenethrough the constricted passageway between the rim of the sealing plateand the bore of the barrel formed an effective plastic seal againstcounter-current flow of vapors of the volatile organic material from themixing and cooling zone of the extruder. The extruder was connected inan arrangement of apparatus similar to that shown in the drawing,wherein the material was forwarded in the mixing and cooling section ofthe extruder under pressure and malaxated into a homogeneouslyheat-plastified mass under pressure and brought to a un form temperaturethroughout just prior to discharge into the atmosphere through amultiple orifice die. The polystyrene was heat-plastified attemperatures between 170 and 220 C. in the first section of the extruderand about 3 inches of water, then passed horizontally through aboutthree feet of water and removed from the cooling bath and passed to acutting device wherein they were cut to a granular form. The extrudedstrands in passing downward through air into the water bath were hotstretched so that the cooled strands of product had a diameter of aboutinch. The product was transparent granules of the polystyrene containingthe isopentane uniformly dispersed throughout. The granules containedapproximately 5.5 percent by weight of the isopentane and had a densityof 0.96. A portion of the product was foamed by heating the same attemperatures between 105 and 110 C. for a period or" 3 minutes. Thefoamed material had a volume 24 times as great as the initial volume ofthe polymeric composition. It was a cellular mass having a densitycorresponding to 2.6 pounds per cubic foot of the foam.

EXAMPLE 2 In each of a series of experiments a thermoplastic polymer anda volatile organic compound as identified in the following table weremalaxated under pressure into a homogeneously heat-plastified mass,extruded into the atmosphere, cooled and ground to a granular formemploying an arrangement of apparatus similar to that employed inExample 1. Table I identifies the polymer starting material and thevolatile organic compound employed as foaming agent and gives the rateof feed of each to the extruder in pounds per hour. The table also givesthe pressure in pounds per square inch gauge pressure of the material inthe extruder just prior to discharge through the extrusion orifice, thetemperature of the extruding material and the temperature of the waterbath which was used to cool the extruded material.

The table gives the percent by weight of the volatile organic compoundin the product and its density. Portions of the product were foamed byheating the same with superheated steam at atmospheric pressure and attemperatures between 105 and 110 C. The products foamed to cellularmasses. The table gives the ratio of the volume of the foam to theinitial volume of the product.

Table 1 Starting Materials Extrusion Conditions Product Run PolymerVolatile Compound Water Volatile Foam N Pressure, Temp, Bath Oom-Density, Volume] lbs./su 0. Temp., pound, gun/cc. Initial Kind lbs/hr.Kind lbs/hr. in. C. Percent Volume Ratio 1 P0lystyrene- .24Isopentana.-- 1.5 850 114 13 5 75 O 96 10 2 -d0 20Dichlorodifluoroethane. 2. 75 1, 000 126 13 12.0 1. 1 5. 5 3Polydichloro Styrene 20 Isopentane 1.25 600 119 13 5. 75 0.96 9.5 4Polyviuyltoluene 30 do 2.25 500 117 23 7.0 0.96 4.5 5 Copolymer of99.94% 20 rlo 2.25 875 117 23 10.0 0.94 4.0

Styrene, 0.06% Divinylbenzene. 6 Polystyrene 30 d0 2.0 1,000 119 49 6.250.90 3.0

was forwarded by pressure of the screw around the seai- EXAMPLE 3 ingplate into the mixing and cooling section of the extruder wherein it wasmixed with isopentane fed into the barrel of the extruder under pressureat a rate of 2.38 pounds per hour. The resulting mixture was blendedunder pressure and cooled to a homogeneously heatplastified mass and wasextruded under a pressure of about 550 pounds per square inch gaugepressure and at a temperature of 131 C. through a die having fortysixinch diameter drill holes, into the atmosphere. The die was positionedat a distance of about one inch above a liquid body of water maintainedat a temperature of 13 C. The strands of the extruded material wereGranular polystyrene having a viscosity characteristic of 22 centipoises(10 weight percent solution of the polystyrene in toluene at 25 C.) wasfed to an extruder at a rate of 20 pounds per hour wherein it was heatplastified and mixed with 10 percent by weight of isopentane and 5percent by weight of acetylene tetrabromide as blowing agent andflame-proofing agent, respectively. The resulting mixture was malaxatedunder pressure and was extruded as a homogeneously heat-plastified massunder a pressure of about 1200 pounds per square inch gauge pressure andat a temperature of 111 C. into the drawn downward away from the die andimmersed under atmosphere and was almost immediately cooled by beingimmersed in water at a temperature of 49 C. then was cut to a granularform employing an arrangement of apparatus similar to that shown in thedrawing. The product was a solid material having a density of about 1.2and contained the isopentane and acetylene tetrabromide uniformlydispersed throughout. A portion of the product was foamed by heating insuperheated steam at atmospheric pressure and at temperatures between105 and 109 C. The foamed volume was 19 times as great as the initialvolume of the unfoamed material.

By procedure similar to that described in the foregoing exampleslatent-foaming polymeric compositions can readily be prepared byemploying a copolymer of from 70 to 99 percent by weight of styrene andfrom to 1 percent of alpha-methyl styrene, acrylonitrile or methylmethacrylate for the thermoplastic copolymer employed in the examples.

This application is a continuation of my pending application Serial No.699,666, filed November 29, 1957, now abandoned.

I claim:

l. A' process for making a latent-foaming polymeric compositioncomprising essentially a normally solid thermoplastic polymer having avolatile organic compound uniformly dispersed throughout, which processcomprises supplying a uniform homogeneously 'heatplastified masscomprising a normally solid thermoplastic polymer and a volatile organiccompound boiling at a temperature not higher than 95 C., and in whichthe polymer is insoluble in intimate admixture with one another undersuper-atmospheric pressure at temperatures between 160 and 280 C.,advancing the heat-plastified mass toward an extrusion orifice, coolingand blending the material during said advancing to a uniform temperaturebetween about 90 C. and a temperature below the heat-plas-tifyingtemperature, extruding the heat plastified mass into a zone ofatmospheric pressure and almost immediately and prior to appreciableexpansion of the extruded material contacting the extruded material withan inert liquid cooling medium and cooling the extruded material to arigid condition at a temperature below C. l 2. A process according toclaim 1, wherein the thermoplastic polymer contains in chemicallycombined form a predominant amount of styrene.

3. A process for making a latent-foaming polymeric compositioncomprising essentially a normally solid thermoplastic vinyl aromaticpolymerhaving a volatile organic compound uniformly dispersedthroughout, which process comprises supplying a uniform homogeneouslyheat-plastified mass comprising a normally solid thermoplastic vinylaromatic polymer containing in chemically combined form a predominantamount of at least one monovinyl aromatic compound of the benzene seriesand a volatile organic compound of the class consisting of saturatedaliphatic hydrocarbons and perchlorolluoro carbons having a boilingpoint not higher than 95 C. and a molecular weight of at least 58, inintimate admixture with one another under superatmospheric pressure andat temperatures between 160 and 280 C., said heatplastified masscontaining the volatile organic compound in proportionscorresponding tofrom 0.05 to 0.3 gram molecular proportion of the volatile organiccompound per 100 grams of the Vinyl aromatic polymer, advancing the masstoward an extrusion orifice, cooling and blending the material duringsaid advance to a uniform temperature between 90 and 130 C., extrudingthe heatplastified mass into a zone of atmospheric pressure and almostimmediately and prior to appreciable expansion of the extruded materialcont-acting the extruded material with an inert liquid cooling mediumand cooling the extrude'd material to a rigid condition at a temperaturebelow 50 C., said cooled mat rial having a density between 0.8 and 1.2.7 'g 4. A process as claimed in claim 3, wherein the Vinyl aromaticpolymer is a polymerized monovinyl aromatic hydrocarbon.

5. A process as claimed in claim 4, wherein the vinyl aromatic polymeris polystyrene.

6. A process as claimed in claim 4, wherein the vinyl aromatic polymeris polyvinyltoluene.

7. A process as claimed in claim 3, wherein the volatile organiccompound is at least one saturated aliphatic hydrocarbon containing from4 to 7 carbon atoms in the molecule.

8. A process as claimed in claim 7, wherein the volatile organiccompound contains 5 carbon atoms in the molecule.

9. A process as claimed in claim 3, wherein the vinyl aromatic polymeris a copolymer of from 99.9 to 99.99 percent by Weight of at least onemonovinyl aromatic hydrocarbon'and from 0.1 to 0.01 percent ofdivinylbenzene.

10. A process for making a latent-foaming polymeric compositioncomprising essentially a normally solid thermoplastic vinyl aromaticpolymer having a volatile organic compound in which the vinyl aromaticpolymer is substantially insoluble uniformly dispersed throughout, whichprocess comprises supplying under superatmospheric pressure attemperatures between 160 and 280 C., a mixture of (1) a heat-plastifiedthermoplastic polymeric material of the class consisting of polymerizedmonovinyl aromatic hydrocarbons of the benzene series, polymerizednuclear halogenated derivatives thereof, copolymers of from 99.90 to99.99 percent by weight of at least one such monovinyl aromatic compoundand from 0.1 to 0.01 percent of a polyvinyl aromatic hydrocarbon andcopolymers of from 70 to 99 percent by weight of at least one suchmonovinyl aromatic compound and from 30 to 1 percent of an alpha-alkylstyrene, and (2) a volatile organic compound of the class consisting ofsaturated aliphatic hydrocarbons and perchlorofluorocarbons having amolecular weight of at least 58 and boiling at a temperature below C.,said mixtur containing the volatile organic compound in proportionscorresponding to from 0.05 to 0.3 gram molecular proportion of thevolatile organic compound per 100 grams of the poly meric material,advancing the mixture toward an extrusion orifice, cooling and blendingthe mixture during said advancing to a homogeneously heat-plastifiedmass at temperatures between 90 and C., extruding the heatplastifiedmass into a zone of substantially atmospheric pressure and almostimmediately and prior to appreciable expansion of the extruded materialcontacting the extruded material with an inert liquid cooling fluid andcooling the extruded material to a rigid condition at a temperaturebelow 50 C., said cooled material having a density between 0.8 and 1.2.

11. A process for making a latent-foaming polymeric compositioncomprising essentially a normally solid thermoplastic vinyl aromaticpolymer having a volatile organic compound uniformly dispersedthroughout, which process comprises supplying a uniform homogeneouslyheat-plastified mass comprising a normally solid thermoplastic vinylaromatic polymer containing in chemically combined form a predominantamount of at least one monovinyl aromatic compound of the benzene seriesand a volatile organic compound of the class consisting of saturatedaliphatic hydrocarbons and perchlorofiuorocarbons having a boiling pointnot higher than 95 C. and a molecular weight of at least .58, inintimate admixture with one another under superatmospheric pressure andat temperatures between and 280 said heatplas-tified mass containing thevolatile organic compound in proportions corresponding to from 0.05 to0.3 gram molecular proportion of the volatile organic compound per 100grams of the vinyl aromatic polymer, advancing the mass toward anextrusion orifice, cooling and blending the material during saidadvancing to a uniform temperature between about 90 C. and a temperaturebelow 9 10 the heat-plastifying temperature, extruding the mixtureReferences Cited in the file of this patent into a zone of atmosphericpressure and almost immediately and prior to appreciable expansion ofthe ex- UNITED STATES PATENTS truded material contacting the extrudedmaterial with an 2,464,746 Gering Mar. 15, 1949 inert liquid coolingmedium and cooling the extruded 5 2,515,250 McIntire July 18, 1950material to a rigid condition. 2,537,977 Dulmage Jan, 16, 1951

1. A PROCESS FOR MAKING A LATENT-FOAMING POLUMERIC COMPOSITIONCOMPRISING ESSENTIALLY A NORMALLY SOLID THERMOPLASTIC POLYMER HAVING AVOLATILE ORGANIC COMPOUND UNIFORMLY DISPERSED THROUGHOUT, WHICH PROCESSCOMPRISES SUPPLYING A UNIFORM HOMOGENEOUSLY HEATPLASTIFIED MASSCOMPRISING A NORMALLY SOLID THERMOPLASTIC POLYMER AND A VOLATILE ORGANICCOMPOUND BOILING AT A TEMPERATURE NOT HIGHER THAN 95*C., AND IN WHICHTHE POLYMER IS INSOLUBLE IN INTIMATE ADMIXTURE WITH ONE ANOTHER UNDERSUPERATMOSPHERIC PRESSURE AT TEMPERATURES BETWEEN 160* AND 280*C.,ADVANCING THE HEAT-PLASTIFIED MASS TOWARD AN EXTRUSION ORIFICE, COOLINGAND BLENDING THE MATERIAL DURING SAID ADVANCING TO A UNIFORMEDTEMPERATURE BETWEEN ABOUT 90*C. AND A TEMPERATURE BELOW THEHEAT-PLASTIFYING TEMPERATURE, EXTRUDING THE HEAT PLASTIFIED MASS INTO AZONE OF ATMOSPHERIC PRESSURE AND ALMOST IMMEDIATELY AND PRIOR TOAPPRECIABLE EXPANSION OF THE EXTRUDED MATERIAL CONTACTING THE EXTRUDEDMATERIAL WITH AN INERT LIQUID COOLING MEDIUM AND COOLING THE EXTRUDEDMATERIAL TO A RIGID CONDITION AT A TEMPERATURE BELOW 50*C.